A banquet hall was unoccupied when its snowy roof caved in early Monday in Elgin. It was the second building collapse in a week in the western suburb. Only the rear wall was left partially standing after the overnight collapse at 216 Prairie St., according to Elgin Fire Department Assistant Chief Rich Carter. “It’s undetermined what caused it, but our best guess is snow on the roof,” Carter said. The building was occupied by Imago Events, which has a wedding banquet hall at that location, according to the company’s website. The building was built in the 1920s. Another building collapse on Saturday was a similar situation, Carter said. Both buildings had snowy roofs that were supported by bow trusses. Neighbors called 911 after hearing both crashes.